Context item always refers to document set?

[xatapult]

Currently the context item only exists when a single document is flowing through the pipeline. Assume this is an XML document:

<p:variable name="doc" as="document-node()" select="."/>

But when a sequence of document is possible and there is no or multiple document(s), there is no context item.

That leads to some weird coding problems. For instance, I want to catch the results on the error port of p:os-exec. What I intuitively do is:

<p:variable name="error-message" as="xs:string" select="string(.)" pipe="error@..."/>

But this doesn't fly because when there is no error, there is no context item... Why? I have to resort to clumsy looking solutions like:

<p:variable name="error-message" as="xs:string" select="string(collection()[1])" collection="true" pipe="error@..."/>

So can't we define that the context item always exists and is always the sequence of documents that's flowing through?

• No document? Empty sequence
• Single document? Just as it is now
• Multiple documents? Sequence of item() representing the documents (in the right order!). So document-node() for documents, maps or arrays for JSON, etc.

In retrospect, isn't the whole thing with making sequence of documents special (the use of the collection attribute) an XProc/XPath 1.0 left-over?

It would also solve #22. You could simply write count(.) to get the number of documents and exists(.) or empty(.) to check whether a document is there.